sounds to me like you may be a POS and are expecting to screw this guy over. 10 years of loyalty may not mean much to you, or your company, but to an honest and respectful business, it does mean something. Most rental properties feel they are worth more than they really are. Sounds to me like yours is worth less.

If he's been on time for 10 years I'd probably just let it go. Try to be the bigger man. You say he's doing all of this over $50, so are you. Just call him and apologize and tell him after rethinking it you're going to waive the fee this time. You'll probably save yourself a lot of headache.